The present invention, in some embodiments thereof, relates to pharmacology and, more particularly, but not exclusively, to a novel methodology for the treatment of inflammatory bowel diseases.
Inflammatory bowel disease, or IBD, is a collective term encompassing related, but distinct, chronic inflammatory disorders of the gastrointestinal tract, such as Crohn's disease, ulcerative colitis (UC), indeterminate colitis, microscopic colitis and collagenous colitis, with Crohn's disease and ulcerative colitis being the most common diseases. Ulcerative colitis is confined to the large intestine (colon) and rectum, and involves only the inner lining of the intestinal wall. Crohn's disease may affect any section of the gastrointestinal tract (e.g., mouth, esophagus, stomach, small intestine, large intestine, rectum and anus) and may involve all layers of the intestinal wall. Both diseases, as well as other IBDs, are characterized by abdominal pain and cramping, diarrhea, rectal and/or intestinal bleeding, weight loss and fever. The symptoms of these diseases are usually progressive, and sufferers typically experience periods of remission followed by severe flare-ups. Less frequent, but also possible, IBD symptoms reflect mucosal inflammation of other sections of the GI tract, such as duodenitis, jejunitis and proctitis.
The goal of IBD therapy is to reduce the extent and symptoms of the inflammation, rather than to actually cure the disease (Kesisoglou and Zimmermann, 2005). Aminosalicylates and corticosteroids are the traditional mainstays of IBD therapy. Immunomodulators (e.g. 6-mercaptopurine, its prodrug azathioprine, tacrolimus), antibiotics, and biological response modulators (infliximab) are also commonly used.
The most commonly used medications to treat IBD are anti-inflammatory drugs such as the salicylates. Preparations of salicylate are effective in treating mild to moderate disease and can also decrease the frequency of disease flares when the medications are taken on a prolonged basis. Examples of salicylates include sulfasalazine, olsalazine, and mesalamine. Particularly, sulfasalazine and related drugs having the bioactive 5-amino-salicylic acid (5-ASA) moiety are widely used to control moderate IBD symptoms and to maintain remission. All of these medications are given orally in high doses for maximal therapeutic benefit. However, treatments with these medications is typically accompanied with adverse side effects such as nausea, dizziness, changes in blood chemistry (including anemia and leukopenia), skin rashes and drug dependence.
Corticosteroids are more potent and faster-acting anti-inflammatory drugs in the treatment of IBD, as compared with salicylates. Prednisone, for example, is a corticosteroid commonly used in the treatment of severe cases of IBD. Nevertheless, potentially serious side effects limit the use of corticosteroids to patients with more severe disease. Side effects of corticosteroids usually occur upon long term use and include thinning of the bone and skin, infections, diabetes, muscle wasting, rounding of faces, psychiatric disturbances, and, on rare occasions, destruction of hip joints.
In cases where IBD patients do not respond to salicylates or corticosteroids, medications that suppress the immune system, namely immunosuppressants, are used. Examples of immunosuppressants include azathioprine and 6-mercaptopurine. However, as immunosuppressants may render the patient immuno-compromised and susceptible to other diseases, the use thereof in the treatment of IBD is not recommended.
IBD presents a challenging target for drug delivery (Klotz and Schwab, 2005). Because the original disease pathogenesis and some of the major pathological manifestations are confined to the GIT tissue, an ideal delivery strategy for IBD should result in an elevated concentration of the therapeutic entity in the diseased intestinal tissue with minimal systemic exposure. For example, studies have shown that for 5-aminosalicylic acid (5-ASA), the therapeutic effect in IBD is directly correlated with the drug concentration in the diseased intestinal mucosa (see, FIG. 1) (Frieri et al., 2000).
Current delivery strategies in the treatment of IBD are based on either a delayed release formulation or a chemical modification of the drug molecule. Delayed release of the drug is typically achieved with polymer coating. For instance, Asacol® is an Edugarit S-coated 5-ASA formulation in which 5-ASA is designed to be released at pH >7, which is found in the ileum and further, Pentasa® is an ethylcellulose-coated 5-ASA formulation in which 5-ASA is continuously release over several hours. The chemical modification approach is focused mainly on increasing first-pass hepatic metabolism and thereby reducing systemic drug levels (e.g., budesonide), or linking the drug (mainly 5-ASA) to a carrier via azo bond to reduce the absorption of the complex in the small intestine and thereby targeting the colon; in the colon, bacterial azo-reductases are able to liberate the free drug from the complex, effectively leading to colonic drug targeting (e.g. sulfasalazine, olsalazine and balsalazide).
All these strategies, however, target a region of the intestine (typically the colon), and not the actual diseased tissue itself. This is disadvantageous with respect to drug therapy and patient care, as it essentially leads to a waste of significant portion of the administered dose, and to increased chances of side effects. Additionally, it excludes the use of these drug products in cases where the inflammation is outside of the particular targeted region, e.g., the small intestine in CD patients.
PLA2 (phospholipases A2) represent a family of enzymes that catalyze the hydrolysis of the sn-2 fatty acyl bond of phospholipids (PL), to liberate a free fatty acid and a lysophospholipid (see, FIG. 2). At least 19 enzymes with PLA2 activity have been identified to date; 10 isozymes are secreted from cells (sPLA2), and the others are cytosolic enzymes (cPLA2), however, by definition, all of them hydrolyze the ester bond at the sn-2 position of PL (Murakami and Kudo, 2002; Touqui and Alaoui-El-Azher, 2001). It has been reported that sPLA2 enzymes do not demonstrate any specific fatty acid selectivity (Kurz and Scriba, 2000; Laye and Gill, 2003).
In the past decade, PLA2 expression in the inflamed tissue of IBD patients, both CD and UC, has been consistently reported to be significantly elevated. In CD, significantly increased gene expression of PLA2 was found in both the small and the large intestinal mucosa with active inflammation (Haapamaki et al., 1999a), as well as significantly higher PLA2 mRNA levels and activity in ileal mucosa from CD patients than from controls (FIG. 3A) (Lilja et al., 1995). In the protein level, the mass concentration of group II PLA2 protein was found to be significantly higher in colonic mucosa of CD patients compared to control (Haapamaki et al., 1998; Minami et al., 1994), and the increased level was correlated with the degree of the inflammatory activity in the intestinal wall (Haapamaki et al., 1998). PLA2 activity in CD patients was measured as well, and was reported to be significantly higher (about 5-folds) than that in control subjects, with an association to the degree of inflammation (see, for example, FIG. 3B) (Minami et al., 1994). The situation was not different in UC; significantly increased gene expression of PLA2 was found in inflamed large intestinal mucosa of UC patients compared to control, with an association between the PLA2 mRNA levels and the degree of inflammation (Haapamaki et al., 1997). The concentration of PLA2 protein in the colonic mucosa of UC patients was found to be significantly higher compared with control (Haapamaki et al., 1999b; Minami et al., 1994), and increased activity in the diseased tissue of UC patient was evident as well (FIG. 3C) (Minami et al., 1994; Peterson et al., 1996). Overall, these data clearly indicate that PLA2 levels are elevated in the diseased IBD tissue, and support the theory that PLA2 is involved in the local and generalized pathological processes of IBD, CD and UC.
The present inventors have previously disclosed an exploitation of the esterase enzyme phospholipase A2 (PLA2) to mechanistically target drug molecules to diseased cells. Thus, the present inventors have designed and investigated a series of conjugates of a phospholipid and the non-steroidal anti-inflammatory drug indomethacin and of a phospholipid and valproic acid, differing in the length of the carbonic linker between the PL and the drug moiety (Dahan et al., 2007; Dahan et al., 2008).
WO 91/16920 discloses lipid derivatives of anti-inflammatory drugs, including aspirin, other salicylates and other non-steroidal anti-inflammatory drugs (NSAIDs), which serve as phospholipid prodrugs that are activated by digestive enzymes such as phospholipase A2 and other phospholipases and lysophospholipases, so as to release the drug and provide a steady level of the drug in the bloodstream while reducing toxicity. According to the teachings of WO 91/16920, the phospholipid prodrugs are useful in treating chronic inflammatory diseases such as rheumatoid arthritis and osteoarthritis.
WO 00/31083 discloses phospholipid derivatives of NSAIDs in which the drug is covalently linked to a phospholipid moiety via a bridging group, and which release the NSAID upon enzymatic cleavage at the diseases site. According to the teachings of WO 00/31083, the bridging group is designed to be sensitive to cleavage by phospholipases such as PLA2 that are specifically elevated at the site of the disease.
Additional background art includes Dahan and Amidon, Am. J. Physiol. Gastrointest. Liver Physiol. 2009; Dahan et al., J. Control. Release, 2007; Dahan et al., J. Control. Release, 2008. Dahan and Hoffman, Drug Metab. Dispos., 2007; Dahan and Hoffman, European Journal of Pharmaceutical Sciences, 2005; Dahan and Hoffman, European Journal of Pharmaceutical Sciences, 2006; Dahan and Hoffman, Pharmaceutical Research., 2006; Dahan et al., Drug Metab. Dispos., 2009; and Dvir et al., CNS Drug Rev. 2007.